The present invention relates to a method of producing a member of recrystallized material (hereinafter referred to as "recrystallized-material-member") and an apparatus used therefor. The present invention also relates to a method of producing a thin film semiconductor which is a recrystallized-material-member used for LSI devices and solar cells, and an apparatus used therefor. Further, the present invention relates to a method of producing the above-mentioned thin film semiconductor having an SOI structure, and an apparatus used therefor.
Further, the present invention relates to a method of heating materials to be heat-treated.
As examples of the recrystallized-material-member obtained by recrystallizing a member of crystalline material (hereinafter referred to as "crystalline-material-member"), there can be exemplified a thin film semiconductor used for LSI devices, solar cells and the like. The thin film semiconductor is usually produced by melting and recrystallizing the crystalline-material-member under optional conditions to increase a size of crystal grains. In many cases, the thin film semiconductor is provided on a substrate and is covered or sandwiched with insulators.
FIG. 13 shows a partial sectional view of one embodiment of the above-mentioned thin film semiconductor. In FIG. 13, numeral 132 indicates a substrate, numeral 133 indicates a first insulator, numeral 134 indicates a thin film semiconductor, numeral 135 indicates a second insulator and numeral 131 shows a deposited layer comprising the substrate 132, the first insulator 133, the thin film semiconductor 134 and the second insulator 135.
Such a deposited layer is heated to recrystallize the thin film semiconductor, and thus the deposited layer having the thin film semiconductor layer is produced.
FIG. 14 shows an explanatory view of a conventional apparatus for recrystallizing a thin film semiconductor and a conventional method of recrystallization using that apparatus. In FIG. 14, numeral 141 indicates a deposited layer comprising a substrate, a first insulator, a thin film semiconductor and a second insulator (In FIG. 14, for the purpose of easy illustration, only the thin film semiconductor is depicted. The thin film semiconductor in the deposited layer 141 comprises the numerals 142, 143 and 144.), numeral 142 indicates a recrystallized zone of the thin film semiconductor, numeral 143 indicates a molten zone of the thin film semiconductor by heat-treating, numeral 144 indicates an unmolten zone of the thin film semiconductor, numeral 145 indicates a susceptor for supporting the deposited layer 141, numeral 146 indicates a melting heater for supplying thermal energy to the thin film semiconductor, numeral 147 indicates an elliptic mirror for focusing energy from the melting heater onto the desired region of the deposited layer 141, numeral 148 indicates an auxiliary line (short dashed line) illustrating a state of energy being focused onto the deposited layer 141 by the elliptic mirror 147, numeral 149 indicates a base heater for heating the whole of the thin film semiconductor to an optional temperature lower than the melting temperature of the thin film semiconductor, and numeral 150 indicates an arrow indicating a scanning direction of the melting heater 146 and the elliptic mirror 147. The deposited layer 141 and the susceptor 145 are provided inside a chamber (not shown in FIG. 14) for the purpose of atmosphere control, prevention of mixing of impurities and foreign matters and confinement of heat.
According to the above-mentioned conventional method, first, the deposited layer 141 supported by the susceptor 145 is heated by the base heater 149 to an optional temperature lower than the melting temperature of the thin film semiconductor. Then the given zone of the thin film semiconductor is melted by, for example, irradiating infrared rays, i.e. generating energy from the melting heater through heating by the melting heater 146, and focusing that energy with the elliptic mirror 147 onto the given zone of the deposited layer 141. Subsequently the melting heater 146 and the elliptic mirror 147 are moved in parallel with the direction of the arrow 150 at a given scanning speed, and thus the above-mentioned zone to be melted can be continuously moved along the thin film semiconductor, thereby continuously melting the given zone of the thin film semiconductor and then solidifying by turns to successively advance the recrystallization by using the formerly solidified zone as a seed for recrystallization. With this recrystallization, crystals having a grain size of several millimeters to several centimeters can be obtained, though it depends on the thickness of the thin film semiconductor and the scanning speed.
However, in case where the zone to be melted is wide, melting of the substrate or peeling off of the insulator tend to arise. Therefore it is necessary to narrow the zone to be melted of the deposited layer 141 where energy from the melting heater 146 is focused (for example, in case where energy is focused on a band-like zone as shown in FIG. 14, it is necessary to narrow the width of the band-like zone to several millimeters.). The thickness of the thin film semiconductor is usually as small as several micrometers to several tens of micrometers. Therefore, it is very difficult to maintain the temperature of the zone to be melted of the thin film semiconductor constant. Also, the above-mentioned zone of the deposited layer, where energy is focused, is required to be continuously moved along the deposited layer (along the thin film semiconductor). For that reason, it is very difficult to measure continuously the temperature of the zone to be melted of the thin film semiconductor.
According to the above-mentioned conventional method, energy outputs of the melting heater 146 and the base heater 149 were controlled by an open-loop control, that is, the thin film semiconductor was melted continuously by setting the energy outputs previously and continuing supply of energy according to the set outputs. However, in such a method, there were cases where (1) the temperature of the substrate 132 (shown in FIG. 13) became unstable, for example, due to wholly nonuniform contact between the susceptor and the thin film semiconductor (there were contacting portions and non-contacting portions) or due to instable atmosphere temperature (atmosphere temperature was not constant throughout the process); (2) variation of the energy outputs from the melting heater 146 and/or the base heater 149 arose during the scanning due to unstable power supply from power source or unstable control signal; (3) variation of a distance between the melting heater 146 and the thin film semiconductor 144 arose during the scanning due to mechanical inaccuracy of an apparatus or vibration of the apparatus itself or from outside the apparatus. In those cases, there was such a problem that the temperature of the zone to be melted of the thin film semiconductor does not become constant.
If such a problem arises, a density of crystal defects of the obtained thin film semiconductor, such as a dislocation cluster, twin, dislocation and sub-grain boundary increases, and thus crystal quality is apt to become nonuniform.
Also, when the temperature of the molten zone of the thin film semiconductor is too low, sufficient melting cannot be carried out, and when too high, for example, in the deposited layer 131 shown in FIG. 13, there is a case where the obtained thin film semiconductor 134 is peeled off from the insulator 133 or 135.
In the thin film semiconductor obtained by such a method as mentioned above, problems with appearance and crystallinity are apt to arise, and the proportion of the portion which can be used as a product is smaller, i.e. yield is reduced.
An object of the present invention is to provide the recrystallized-material-member having a uniform crystal quality by recrystallizing a crystalline-material-member.